Billiemains Fort is the remains of an ancient castle. It once had a shared army with Bonkyl and Ferney but was destroyed after the Rough Wooing in May 1544.
South of Auchencrow towards Chirnside, during the war of the Rough Wooing, Billie was burnt in May 1544 during the withdrawal of Lord Hertford's army from Edinburgh. The castle tower, "Byllye tower 9 miles from Berwick on the edge of Lammermore, between Angus's barony of Boncle, and Coldingham" was captured on Candlemass Day in January 1548 by the English soldier Thomas Carlile, who overcame the guard with 10 companions dressed "in maner of Skottes." He garrisoned the tower with 50 horsemen.
Billie Castle was mentioned with two other neighbouring strongholds Bonkyll Castle and Blanerne Castle in a prophetic rhyme referring to their construction in the time of David I;
Bunkle, Billie and Blanerne
Three castles strong as irne,
Built when Davie was a Bairn,
Theyll all gang doon,
Wi Scotland's Croun
An ilka ane shall be a cairn. Tweezers needed.